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Descriptions

The western Taylor Park area covers about 65 square
miles on the western flank of the Sawatch Range. It is
underlain chiefly by Precambrian rocks, partially covered
on the east by glacial debris and overlapped on the west
and south by Paleozoic sedimentary rocks.
The Precambrian rocks include a group of metasedimentary
rocks of an undetermined age greater than 1700 m.y.
The metasedimentary rocks include five mineralogically distinct
units, quartzite, quartz-muscovite schist, quartz-epidote
schist, quartz-plagioclase-biotite schist, and
quartz-biotite-microcline-sillimanite schist. The higher
grade sillimanite-bearing biotite schists are restricted to
the western half of the map area and closely associated
with the Forest Hill granitic rocks.
The metasedimentary rocks were intruded twice during
Precambrian time. The oldest intrusive event resulted in
syntectonic emplacement of granodiorite and biotite tonalite
rocks. These rocks correlate with the 1700 m.y. old
Denny Creek granodiorite gneiss and Kroenke granodiorite
which are mapped and informally named in the adjoining
Mount Harvard quadrangle.
The second, post-tectonic, igneous event produced
granitic rocks that are dated at 1030 m.y. by Rb-Sr methods.
These rocks include two comagmatic granitic phases,
the Forest Hill porphyritic granite and the Forest Hill
cataclastic granite. A third phase, the Forest Hill hornblende
granodiorite, intrudes the porphyritic granite and,
therefore, is younger than the granitic phases.
The 1030 m.y. age is very significant because the only
other 1000 m.y. old intrusive rocks in Colorado (the Pikes
Peak batholith) are restricted to the Front Range.
Paleozoic sedimentary rocks are exposed along the
western and southern margins of the map area. They range
in age from Cambrian through Permian.
Tertiary igneous rocks, occurring as plugs, dikes and
flows, crop out locally. Two major episodes of Tertiary
activity occurred in the region, one during the Laramide
orogenic event and the other during Oligocene time. The
Tertiary rocks in the map area were formed during the later
igneous event.
The principle structural features of the area include:
(1) northeast-trending Precambrian shear zones and faults,
(2) northwest-trending folding and faulting, (3) east-west-trending
tear faults in the Paleozoic rocks along the western
margin of the map area. Although the northeast and
northwest-trending structural trends originated during the
Precambrian, reactivation along these zones of weakness
probably occurred into mid-Tertiary time.